Field of the Invention
The invention relates to an apparatus and a method for the contactless measurement of a rotation angle.
Brief Description of the Related Art
The contactless measurement of a rotation angle with the aid of the Hall effect is known. For example, from the publication by Reymond, S. et al., “True 2-D CMOS Integrated Hall Sensor”, IEEE SENSORS 2007 Conference, pages 860-863, an apparatus is known for the contactless measurement of a rotation angle, having a semiconductor substrate wherein as magnetic field sensors 64 so-called vertical Hall sensors are integrated. The magnetic field sensors in this publication are arranged at equal mutual intervals on a circular path disposed in the chip plane of the semiconductor substrate. The vertical planes where the magnetic field sensors extend are arranged respectively radially to a notional center axis extending through the center of circle of the circular path and being arranged orthogonally to the chip plane. The magnetic field sensors are so connected to a scanning device that measuring signals of the individual magnetic field sensors are connectible consecutively to a differential output connector for a rotation scanning signal. The values of the magnetic field sensors accordingly are read out in cyclically rotating fashion.
European patent no. EP 2 149 797 (Micronas GmbH) discloses an apparatus for measuring an angle wherein a magnetic field is arranged in a plane. The apparatus has at least two magnetic field sensors that are arranged with their measurement axes in and/or parallel to the plane and are oriented mutually transversally.
Metz et al. also describe the contactless measurement of a rotation angle in the publication “Contactless Angle Measurement using Four Hall Devices on Single Chip”, Transducers, 1997 International Conference on Solid-State Sensors and Actuators, Chicago, 16-19 Jun. 1997. This publication shows four lateral Hall sensors arranged at equal mutual intervals on a circular path disposed in the chip plane of the semiconductor substrate. A permanent magnet having two poles is attached at the end of a rotating axle and generates a magnetic field in the Hall sensors. The same apparatus is described in the European Patent No. EP-B-0 916 074.
The known apparatus have in common that a permanent magnet is mounted on a rotatable element and generates a magnetic field that is captured by the Hall sensor. A problem in such apparatus are magnetic interference fields in the surroundings of the Hall sensor. A signal processing processor needs to effect a compensation of the measuring values received from the Hall sensor, in order to compensate these magnetic interference fields. This compensation is possible in a relatively simple fashion for a homogeneous background field. The compensation for a magnetic field that is generated by current in an adjacent conductor is more extensive, since the compensation also has to consider the field gradient of the generated magnetic field.
Modern cars have numerous current-carrying conductors causing such magnetic fields. A complete shielding of these magnetic interference fields in the vicinity of a rotation-angle measurement device is impossible.